1. Technical Field of the Invention
The present invention relates generally to a gas sensor which is installed, for example, in an exhaust system of automotive internal combustion engines to measure a specified component of exhaust emissions, and more particularly to an improved structure of such a gas sensor which is designed to ensure desired crimping of a sensor housing to establish a higher degree of gas-tight seal between the housing and a sensor element.
2. Background Art
Typical gas sensors installed in an exhaust system (e.g., an exhaust manifold or exhaust pipe) of automotive internal combustion engines are constructed to have a sensor element fitted hermetically within a hollow cylindrical housing. Such fitting is achieved by crimping or bending an open end portion of the housing to bring the sensor element into constant abutment with an inner wall of the housing. The sensor element has formed therein an inner chamber used as a reference gas chamber into which air is admitted as a reference gas. An outer and an inner electrode are affixed to an outer and inner wall of the sensor element. The inner electrode is exposed to the inner chamber of the sensor element, while the outer electrode is exposed to a measurement gas chamber defined around the sensor element to measure the concentration of a specified component of exhaust gas of the engine flowing into the measurement gas chamber. The crimping of the open end portion of the housing also establishes a gas-tight seal between the sensor element and the housing, that is, between the measurement gas chamber and the reference gas chamber.
U.S. Pat. No. 6,303,013 B1 to Watanabe et al., assigned to the same assignee as that of this application, teaches installation of a sensor element within a housing using the crimping techniques, as described above. The housing, as disclosed in Watanabe et al., is constructed to have an annular extension to be crimped. The annular extension has a wall tapering toward an open end of the housing and dimensions selected to avoid bulging of the annular extension after being crimped.
The tapered wall of the annular extension has a maximum thickness which is more than twice a minimum thickness thereof. Specifically, the annular extension has greatly varying thickness, thus resulting in a difficulty in deforming the annular extension uniformly. Particularly, use of a greatly worn crimper or dimensional errors in the annular extension results in a difficulty to bend the annular extension to 90°, which usually leads to a lack of adhesion between the housing and the sensor element, that is, gas-tight seal between the measurement gas chamber and the reference gas chamber.